AB-INITIO STUDY ON TRANSITION-METAL CARBENE CATIONS

The geometries and bonding characteristic of the first-row transition metal carbene cations MCH2+ were studied by ab initio (HF/LANL2DZ). Al l of MCH2+ are coplanar. In the closed shell structures the sigma and pi obitals are all doubly occupied, Therefore, they are ''perfect'' do uble bonds, but in the open shell, they are ''imperfect'', because the re are only three electrons in sigma and pi orbitals, It was mainly th e pi-type overlap between 2p(x) of C and 4p(x), 3d(xz) of M that forme d the pi orbitals, The dissociation energies of C = M+ bond appear per iodic trends from Sc to Cu. The bond dissociation energies of C = M+ c alculated at PMP3/LANL2DZ level are basically closed to the experiment al values.